Sweating the small stuff ... or not...

When someone you love does something that is not necessarily bad but you feel is wrong and goes against your beliefs... and they know your beliefs ... what do you do about it? Do you take up the issue with them or just let it slide?What if you're really bothered by it? What if the person tells you that they will never do this thing again? Should you just believe them and let it go, knowing that they might not necessarily be telling you the *exact* truth?Is it worth duking it out over something that in the general scheme of things doesn't matter all that much? Won't that cause more harm than good?